I noticed that, while there used to be religious wars, for the most part these days, what gets people to die for no good reason is nationalism.

Don't both of religion and nationalism fall under the broader umbrella of tribalism? It's plausible to me that without either one there would be some other sort of tribalism with adverse effects on global welfare. People might not die as a result but I don't think that there's reason to think that the aggregate negative effect would be smaller.

Now, if what replaced them was some sort of ideology of the type "equal consideration for all" that filled the vaccum left over by politics/religion then that would be different. I have little sense for how likely this would be.

I'm not sure what the best attitude is-- I don't think we can dispense with government these days, but on the other hand, I don't think law-abidingness and patriotism should be put very high on the list of virtues.

What sort of law-abidingness do you have in mind here? Obeying military drafts?